Significant research has focused on developing methods to incorporate clays and other hydrophilic fillers into hydrophobic polymers to increase mechanical and barrier properties of composites and nanocomposites. One approach has been to treat the hydrophilic filler surface to render it compatible with hydrophobic materials such as polyolefins and waxes. Organoclay fillers are commonly subjected to this treatment. Generally, this surface treatment consists of an adsorbed monolayer of a high-molecular-weight quaternary amine, such as dimethyl dihydrogenated tallow amine. The surfactant adsorption takes place via an ion-exchange reaction involving the negatively charged basal surface of the clay platelets.
The simple mechanism in which organoclays and other fillers can improve barrier properties in the hydrophobic polymer relies on the high aspect ratio of the filler to impart a tortuous path that retards the transport of diffusing species like oxygen or water vapor. In a strictly tortuous path mechanism, all diffusing species would be retarded to the same degree. However, theoretical barrier properties are commonly missing in actual experimentation and composite and nanocomposite performance has not always lived up to expectations. It is typical to have barrier improvements of only two- to four-fold.
To overcome the difficulties in dispersing fillers in hydrophobic polymers like the polyolefins, researchers have used functionalized polymers, like maleated polyethylene and polypropylene, as dispersants. Although polar functional groups can interact with the filler surface and compatiblizing agents can promote dispersion, this approach to nanocomposite formation has provided only modest improvements in the mechanical properties of polyolefins. Accordingly, there is a need for a rational approach to the design of new surfactant surface chemistries that enable the preparation of composites and nanocomposites which demonstrate significant improvements in physical properties such as increased mechanical and barrier performance.